WO2002019613A1

WO2002019613A1 - Method for generating unchallengeable signatures, in particular by an integrated system, and integrated system therefor

Info

Publication number: WO2002019613A1
Application number: PCT/FR2001/002720
Authority: WO
Inventors: Michel Hazard
Original assignee: Cp8 Technologies
Priority date: 2000-08-31
Filing date: 2001-08-31
Publication date: 2002-03-07
Also published as: FR2813467A1; TW535380B; AU2001287797A1; FR2813467B1

Abstract

The invention concerns a method for generating unchallengeable signature with a smart card (CPi). The latter stores in a storage unit (M) two pairs of so-called mother keys and two diversified keys (dKS1(i) and dKS2(i)) obtained from said pair of keys and an identifier, by applying a triple DES cryptographic algorithm and a certificate generated by a certification authority based a private key of said authority, a public key and by applying a RSA cryptographic algorithm. The signature (SIGNi) is obtained from the two diversified keys (dKS1(i) and dKS2(i)) and data (MSG) to be transmitted by applying a triple DES (3). In a preferred embodiment, two authenticating additional keys are stored in the storage unit (M). Said keys are generated by the certification authority and serve to generate data authenticating the signature, by applying a triple DES.

Description

PROCESS FOR GENERATING NON-REPUDIABLE SIGNATURES,

IN PARTICULAR BY AN ON-BOARD SYSTEM, AND SYSTEM

ON BOARD FOR THE IMPLEMENTATION OF THE PROCESS

The invention relates to a method for generating non-repudable signatures, in particular by an on-board system with an electronic chip.

The invention also relates to an on-board system for implementing the method, in particular a smart card. In the context of the invention, the term "on-board system" must be understood in its most general sense. It relates in particular to all kinds of light terminals provided with an electronic chip, and more particularly to the smart cards themselves. The electronic chip is provided with means for recording and processing digital data, for example a microprocessor for these latter means.

To fix the ideas, and without this limiting in any way its scope, we will place ourselves below in the case of the preferred application of the invention, namely applications based on smart cards, unless stated opposite. In recent years, the exchange of documents in electronic form has greatly increased, in particular via the Internet. However, these exchanges pose several problems. In particular, as in the case of documents in traditional form, that is to say in particular in paper form, it is generally necessary to affix a signature thereto, and above all that this signature unambiguously identifies the sender of the document and is not repudiable by its recipient.

Until recently, only§ "paper" documents could prevail. In many countries, the law requires an original handwritten signature. However, in an electronic environment, the original of a document, for example a contract, is in no way different from a copy.

However, there are technologies which make it possible to fulfill all or part of the functions perceived as characteristic of a traditional handwritten signature. These technologies generally implement encryption techniques, whether or not associated with authentication certificates. The electronic signature is a binary sequence usually obtained by encryption of the message transmitted using a particular cryptology algorithm and signature keys. It should be understood, however, that the message itself can be transmitted in clear if there are no specific confidentiality needs. This is a technique called "sealing". The message and the signature are transmitted to the recipient, possibly accompanied by elements of encryption or verification keys in certain cryptographic processes implementing a so-called public key. The recipient uses the signature and the message transmitted using the same algorithm and the aforementioned public key, which allows him to verify the authenticity of the sender's signature. Incidentally, the process guarantees the integrity of the message transmitted. Indeed, if it were to be accidentally or maliciously corrupted, the decryption makes it possible to highlight this dysfunction.

Some countries, such as Germany, Italy, Denmark, Europe, some states in the United States or Canada (Quebec) have legalized electronic signature procedures. At the end of 1999, the European Parliament and the Council of the Union

Europeans have issued a directive which will have to be transcribed into the national laws of the member countries (article 13). In article 1 of this directive, 1 ^alinéar paragraph, it is stated that "the objective of this directive is to facilitate the use of electronic signatures and to contribute to their legal recognition. It establishes a legal framework for signatures electronic and certain certification services in order to guarantee the proper functioning of the internal market. "

In Article 2, an "electronic signature" is defined as follows: "data in electronic form, which is attached or logically linked to other electronic data and which serves as an authentication method".

There are two types of electronic signatures, one of which can be described as "simple". The second is called "advanced" in the Directive. It is an electronic signature "which meets the following requirements: a) be linked only to the signatory; b) allow the signatory to be identified; c) be created by means that the signatory can keep under his exclusive control; and d) be linked to the data to which it relates in such a way that any subsequent modification of the data is detectable ".

The invention relates more particularly to the second type of electronic signature. To do this, it is necessary to have recourse to secure devices, implementing a data encryption (signature) process, so-called "qualified" certificates and an authority, called "certification service provider" in the directive. , which will be called hereinafter "certification authority". The certification authority notably generates a public key used in the aforementioned process by smart cards.

Indeed, in practical terms, asymmetric cryptographic methods must be used. According to these methods, a private, that is to say secret, signature key is held by the signatory, and a public signature verification key. In reality, in smart card-based applications, the private key is stored in a non-volatile memory area of the signatory's smart cards, memory type "ROM", "EEPROM" or equivalent.

Asymmetric cryptographic processes are deemed to be non-repudable because the signature verifier, due to the characteristics inherent in these processes, does not know how to sign.

To fix the ideas, an example of a well known and widely used asymmetric cryptography method is constituted by the so-called "RSA" method (from the name of its inventors Rivest, Shamir and Adleman). A description of this process can be found in US-A-4405829. Although effective, asymmetric cryptographic methods are not without drawbacks. They are indeed delicate and costly to implement. First, it is necessary to manage and generate as many pairs of private / public keys as there are users to provide with this electronic signature instrument.

Second, asymmetric cryptography requires significant IT resources, at least compared to those usually offered by an electronic chip. It is in particular necessary to provide an arithmetic co-processor to carry out the encryption / decryption calculations.

It follows that the cost of electronic chips with the computing power necessary for asymmetric cryptography is significantly higher than the traditional chips used to date by all other applications. However, cost considerations, for a very widely distributed component, are essential.

One could think of having recourse to symmetric cryptographic methods, less demanding in computing resources. However, the latter, by their own characteristics, cannot guarantee the condition of "non-repudiability" sought, because the signature verifier can also sign, since it is a priori in the same conditions as the signatory. The invention aims to overcome the drawbacks of the methods and devices of the known art, some of which have just been mentioned, while satisfying the needs which are felt.

The object of the invention is to provide a method for generating non-repudable signatures, specially adapted to applications using light terminals such as on-board electronic chip systems, and more particularly chip cards, one of the characteristics of which is offer limited IT resources.

To do this, according to an advantageous characteristic, the method according to the invention associates symmetric cryptography with asymmetric static cryptography, it being understood that the operations implementing this latter method are not carried out in the on-board terminal. he It follows that it is not necessary to provide it with increased computing power, in particular to install a mathematical co-processor.

In a first embodiment of the invention, the method comprises a preliminary phase comprising the following main steps:

1. All smart cards are provided with two pairs of so-called "mother" signature keys, the two pairs of keys being identical for all smart cards.

2. Each smart card also receives two diversified w keys specific to each smart card, calculated from these pairs of "mother" keys and an identifier specific to the smart card in question (and / or any other information identifying the carrier) and contained therein. The calculation of the diversified keys is carried out by using a symmetric cryptographic method, preferably, but not exclusively, by using the so-called "triple DES" method.

(for "Data Encryption Standard").

3. The identifier (and possibly other information) of the smart card is (are) certified by a private (ie secret) key held by an authority known as "certification" . This certificate

20 accompanies the identifier in the smart card and constitutes

"authorization to sign" for the holder of the smart card. The certificate is calculated by using an asymmetric type of cryptography process, preferably the so-called "RSA" process mentioned above. It should however be understood that the necessary calculations are

25 carried out by the certification authority, which can have powerful IT resources and not by smart card. More specifically, the certificate is calculated from the identification data of the smart card and / or of its holder using a private key, the latter being the property of the certification authority.

In applications based on smart cards, this preliminary phase is usually carried out during the so-called "personalization" operation of smart cards. The public certification key is available for the control of certificates by the certification authority and for the control by each of the owners of a signature instrument. It can be, in a first variant, all users with a smart card, or, in a second variant, only users belonging to the same group. In the latter case, the user population is split into at least two distinct groups.

The aforementioned "DES" algorithm was published in 1977 by an official American body, the "NBS" ("National Bureau of Standards"). As an example, a description of this algorithm can be found in the article by Jean-Pierre TUAL, entitled "Cryptography", published in "The Engineering Techniques", volume H2, pages 248-1 to 248- 29.

Similarly, an example of the implementation of certificates is described in the article by Gérard RIBIERE, entitled "Electronic and security certification", published "Les Techniques de l'Ingénieur", volume H2, pages 258-1 to 258-11 .

The subsequent steps, which can be described as operational, include at least the generation of a signature when a message or more generally of an electronic document is sent by one of the smart card owners. , which we will call signatory.

The signature is calculated by encrypting the data to be transmitted using the aforementioned diversified keys, using a symmetric cryptographic algorithm, preferably the triple "DES" as indicated above. Reconstitution and verification of the signature is carried out by an operation identical to encryption, by one or more recipients, using the diversified keys of the signatory, reconstituted by the recipient (s), and using the same symmetric algorithm. . The signatory also transmits his certificate and the identification data used to calculate it in step 3.) of the preliminary phase. This certificate is verified by the recipient (s) using the aforementioned public key. An asymmetric algorithm is used. The necessary calculations can be carried out by a host terminal of the smart card. According to a second embodiment of the method according to the invention, it also includes most of the steps of the preliminary phase. However, one of the two diversified keys is obtained from one of the two pairs of "master" keys and identification data of a recipient, and no longer of the sender as in the first variant. According to this variant, only this recipient is then able to verify the signature of the issuer. With this exception, the verification is carried out in the same manner as above.

It can be seen that, in these two embodiments, all the smart cards have the two pairs of mother keys, which can be weak from a security point of view.

Also, in a preferred variant, compatible with the two embodiments, so as to increase the robustness of the method, a pair of diversified keys is added to each of the smart cards resulting from the diversification of two pairs of authentication keys belonging to the certification authority. This operation is carried out during an additional stage of the preliminary phase. The keys of each smart card are calculated using a symmetric algorithm and an identifier specific to this smart card. As before, the symmetric algorithm is preferably a triple "DES". From the diversified keys resident in the smart card and the previously generated signature, using a symmetric algorithm, the smart card generates additional data which will be called hereinafter "signature authentication data" . This data is also transmitted to the recipient (s). This (these) last (s) little (come) submit them to the certification authority which can in turn authenticate them by return.

In a further preferred embodiment, there is advantageously provided a signature generation counter used to secure the generation of signatures and ensure traceability, for example to detect different signatures bearing the same number. The meters are also resident in smart cards and can optionally be used for the initialization of any data signature. The main object of the invention is therefore a method of generating a signature which cannot be repudiated by a first entity of a set, in particular by an on-board system with an electronic chip comprising at least non-volatile memory means and calculation means, said signature being intended to be disseminated and verified by at least one of said entities of the set, characterized in that it comprises a preliminary phase comprising at least the following steps: the storage in said non-volatile memory means of two pairs of so-called "mother" signature keys, common to all of said entities; generation, from at least one of said pairs of "mother" signature keys and a unique identifier, specific to said first entity, of a first so-called "diversified" signature key, by application of an algorithm symmetric cryptography and the storage of said diversified key in said non-volatile memory means; storing said unique identifier in said non-volatile memory means; the generation by an additional entity called "certification authority" of a certificate constituting an authorization to sign for said first entity, said certificate being obtained from at least said identifier and from a private encryption key held by said authority certification, by applying an asymmetric cryptography algorithm, and storing said certificate in said non-volatile memory means; and - the distribution, by said certification authority, of a public signature verification key to all or part of said entities of the set, and a subsequent phase comprising at least the following steps: - the generation of said non-signature repudiable from said first diversified signature key, from a second diversified signature key and from data to be transmitted intended for at least one said entities of the set, by application of a symmetric encryption algorithm; and the distribution to at least one of said entities of the set of at least said data, said signature, said identifier and said certificate.

The invention also relates to an on-board electronic chip system for implementing this method, in particular a smart card.

The invention will now be described in more detail with reference to the accompanying drawings, among which: FIG. 1 schematically illustrates the architecture of a smart card for generating a non-repudiable signature according to the invention;

FIG. 2 schematically illustrates the generation of a so-called diversified signature key for the smart card of FIG. 1 from a pair of so-called "mother" signature keys and an identifier of the smart card; FIG. 3 schematically illustrates the process for generating a non-repudiable signature according to a first embodiment of the method according to the invention; FIG. 4 schematically illustrates the process of generating so-called signature authentication keys by an entity called the certification authority; FIG. 5 schematically illustrates the process for generating a non-repudiable signature according to a second embodiment of the method according to the invention; FIG. 6 illustrates the process of generating so-called authentication data from the aforementioned authentication keys and signature; - Figure 7 schematically illustrates the different data transmitted by a signatory smart card; FIG. 8 schematically illustrates the step of verifying a signature generated according to the first mode of generation of non-repuditable signatures;

- Figure 9 schematically illustrates the step of verifying a signature generated according to the second mode of generation of non-repudable signatures; and

- Figure 10 schematically illustrates the authentication process by the aforementioned certification authority of a signature generated by a smart card. We will now describe in more detail a preferred embodiment of a method for generating non-repudable signatures according to the invention, according to several variants.

As has been indicated, to fix the ideas, without limiting in any way the scope of the invention, we will place ourselves in the case of an application based on smart cards. The latter's electronic chip usually comprises calculation means, comprising for example a microprocessor, and memory means, both live and non-volatile. Such architecture is well known to those skilled in the art and there is no need to describe it further. FIG. 1 schematically illustrates the architecture of a smart card CP „i being an arbitrary index identifying one of the smart cards of a set of n smart cards CPi to CP _n (not shown). In FIG. 1, only the non-volatile memory, marked M, has been represented. It can be a memory of type "ROM"("Read-OnlyMemory", read only), a memory of type "EEPROM" (Electrically Erasable Programmable Read Only Memory ", but re-programmable) or any other memory of a similar type.

During a preliminary phase, advantageously during the so-called "personalization" phase of the chip card CP „, M |, M ₂ , M ₄ and Λ are recorded in predetermined memory positions, respectively in the example. describes, two pairs of so-called "mother" keys, MKS ^ and MKSπ, on the one hand, and

and MS ₂₂ , on the other hand. These "mother" keys are common to all smart cards, CP-i to CP _n . According to a first alternative embodiment of the method according to the invention, a user Uj, that is to say the holder of the chip card CP _h, signs a message or transmitted data. All other users can verify this signature. To do this, two diversified keys, dKS ^ and dKSz ^, respectively, are calculated and stored in memory positions, and M ₆ , for example. This calculation, performed outside the smart card CPj, implements a symmetric algorithm. Preferably, it is a triple "DES". We will also assume below, each time we use a symmetric algorithm, that it is also the triple "DES", which we will denote below "T-DES" by simplification.

Figure 2 schematically illustrates the calculation of the dKS ^ key. The triple "DES", referenced 1, comprises three stages in cascade 10 to 12. For example, stages 10 and 12 carry out a "DES" called "direct". The signature key used for these two stages is, again in the example, the key S ₁₁ . The intermediate stage 11 performs a so-called reverse "DES", which will be denoted "DES ^'1 ". The signature key used for this stage is the key Λ- S ₁ 2. At the input of the first stage 10, an identification data ID is injected, - from the chip card CPj and / or from its bearer U, - ( figure 1). This identification data ID, - can be unique or from several separate data, for example concatenated, with possibly filling data to obtain a binary word of predetermined length. In FIG. 1, two sources of identification data have been shown, denoted Info and Div (number of the smart card CP _h, etc.). These data are also resident in the smart card CP, - and, in the example illustrated, recorded in the positions M ₇ and M ₈ of the memory M.

The output of stage 10 is transmitted to the entrance of stage 11 and the output of stage 11 is transmitted to the entrance of stage 12. Finally, at the exit of stage 12, we obtain the diversified key dKS ^, specific to the chip card CP _/ , diversified key recorded in the memory position M ₃ as indicated. The calculations are carried out in a secure environment, for example by an entity that will be called "the inserter", outside of the chip card CP ,. Module 1 for the implementation of "T-DES" can either be of the "hardware" type (specialized circuits) or use software. The dKS ₂ (i _{) key} is obtained identically and there is no need to rewrite the process.

If we refer again to FIG. 1, in addition to these various data, a CTA certificate is calculated by a so-called CA certification authority. To do this, this last entity CA implements, according to one aspect of the method according to the invention, an asymmetric algorithm, referenced 2, preferably the aforementioned "RSA" algorithm. Identification data ID, of the smart card CP, are encrypted using a private key, property of the certification authority CA, which will be noted KA.

In the example illustrated by FIG. 1, the result of the encryption operation, that is to say the CTA certificate, is recorded in the memory position M ₉ .

The CA certification authority also distributes a public signature verification key, associated with the private key K _A and which will be called Kp below, to all the smart cards. It has been assumed, up to this point in the description, that all the users U, - possessors of a chip card CP, were part of a single group, and therefore that the public key Kp was set to available to all these users U, -. According to another variant of the embodiment of the method, it is possible to divide all of these users into at least two groups (not shown). Each group will therefore have at its disposal a public key distinct from that of the other groups: C _p1 , Kpz, ..., K _pm , if we assume that m is the number of distinct groups.

FIG. 3 schematically illustrates the generation of a signature, referenced SIGNj, by the smart card CP ,. It is assumed that the bearer U, - of the card CP, - wants to send a message MSG which must be signed. To do this, the message MSG produced by known data processing means, for example the host terminal T of the smart card CP „is transmitted at the input of a" T-DES ", referenced 3, or any other similar symmetric algorithm. In a manner known per se, the MSG message can be subjected beforehand to a so-called "hashing" operation. The logical architecture of this "T-DES" 3 is identical or at least quite similar to that described with regard to FIG. 2. The key used for the direct "DES" stages is, for example, the key

and the key used for the stage "DES ^{" 1} "is the key dKS _{2 (} i ₎ . Since it is a symmetric algorithm, it is not necessary to have powerful means of calculation. the signature can therefore advantageously be carried out inside the chip card CP „using the standard calculation means at its disposal (not shown). It follows that, although for reasons of clarity in the drawing, the calculation means 3 have been shown in the figure on the outside of the chip card CP, -, it should be understood that they are preferably installed in the electronic chip thereof. these are not usually specific circuits, but it is preferable to calculate the signature SIGN, using software, stored in memory M, cooperating with the abovementioned standard calculation means.

It can be seen that the diversified keys, dKS ^ and dKS _∑ ^, that is to say the secret specific to each of the smart cards CP ,, are not revealed to the outside world. However, all CP smart cards have the two pairs of signature keys in their so-called "mother" form. If these keys are "broken", the overall security of the process is jeopardized. Also, to "harden" the process vis-à-vis external attacks, we add in each of the chip cards CP, - a pair of additional diversified signature keys, which we will note dKSA ^ and ûf S-4 ₂ (,), respectively. These keys are themselves derived from the diversification of two pairs of signature authentication keys belonging to the CA certification authority.

(figure 1). The usefulness of these keys will be explained in more detail below.

Figure 4 schematically illustrates the process of generating additional diversified keys, dKSA ^ and dKSA2 (, The so-called "signature authentication key pairs", MKSA and MKSA ^, MKSA21 and MKSA22, respectively, are passed to the key entries modules implementing a symmetric algorithm, preferably a "T-DES", denoted l 'and 1 ". At the input of data, an identifier ID is injected, - characterizing the smart card CP. The process of calculating the keys dKSA ^ and dKSA ₂ {i) is identical, or at the very least similar fact to that (figure 2: 1) used to calculate the diversified keys dKS ^ and dKS _∑ ^. We can also use the same circuits, if they are specific electronic circuits, or the same software .

As for the diversified keys, - KS ^ and dKS _∑ ii), the calculation is carried out during a preliminary phase, in a secure environment, for example during the phase called "personalization" of the smart card CP ,. The results w of the calculations, that is to say the signature authentication keys dKSA ^ and dKSA _{2 (} i ₎ , are also recorded in the memory M of the smart card, in the positions / W-ι ₀ and Mu (see also Figure 1).

According to this preferred variant of the method, uncovering the secret of a chip card CP, - then becomes as difficult as obtaining the private key of a

15 smart card which would be equipped with a dynamic asymmetric cryptography algorithm.

In another variant of the signature generation method, a signature generation counter 4 is advantageously provided, the output of which is denoted CGS. Counter 4 is used to secure the 0 generation of signatures and to ensure traceability (different signatures with the same number). If we refer again to Figure 3, we see that the CGS output is transmitted to the data input of "T-DES" 3. In practical terms, it is a binary word which can be concatenated with the message to sign MSG. This counter 4 is also installed in the

25 smart card CPj and optionally serves to initialize any signature of data. It may be a hardware component, for example belonging to the circuits of the calculation means of the electronic chip of the chip card CPj. Counting (word CGS) can also be obtained by software means.

We will now describe schematically a second embodiment of the signature generation method with reference to FIG. 5. According to this embodiment, one of the diversified keys, for example the key, now referenced dKS ' ₂ (j), is obtained using data from diversification of another smart card, of the group to which the smart card CPj belongs if there are several distinct groups, for example the identification data ID _j of the smart card CPj, and not from the data of identification IDj of the signatory smart card CPj. With the exception of this characteristic, the other phases and stages are identical to those which have been described for the first embodiment. It is therefore unnecessary to re-describe them in full. Likewise, this embodiment is compatible with the use of signature authentication keys, dKSA ^ and dKSA ₂ ^, and with the use of a signature generation counter 4 producing the word CGS.

According to this embodiment, precisely because of the aforementioned characteristic, only the recipient U _j , that is to say the owner of the smart card CP _j, is able to verify the signature of the transmitter Uj, noted SIGN'j in FIG. 5. It is interesting to note that this last characteristic is not offered by the conventional methods of dynamic asymmetric cryptography used for the generation of non-repuditable signatures according to the known art.

It is assumed that, as before, the diversified key dKSi (,) has been calculated and recorded in the memory M of the smart card CP ,. at position M, during the preliminary phase. To do this, identification data IDj specific to the smart card CPj were used.

The diversified signature key dKS ′ ₂ (j) is calculated from the pair of “mother” signature keys MKS _∑ i and MKS ₂₂ , as before, but using the identifier ID _j from the card to CPj chip, identifier recorded in one or more positions of the memory M 'thereof, in a similar manner to the identifier IDj for the chip card CPj. The calculation of the signature key is accomplished by use of a "T-DES", referenced 3 ', receiving on these key inputs, key mothers _Σ i MKS and MKS _22, and in data entry, the aforementioned IDj identifier. The output represents the diversified signing key dKS ' ₂ (i).

During the signature generation step, now referred to as SIGN'j, the process implemented is identical to that of calculating the signature SIGNj in FIG. 3. To do this, we use an algorithm symmetrical, preferably the "T-DES" algorithm (module 3), except for the fact that the key dKS ' _{2 (j)} is calculated differently, as has just been shown. At data entry, the message to be signed MSG is injected, and optionally the CGS signature count word (counter 4: FIG. 3).

In this embodiment, it is necessary to obtain a certified identifier of the recipient.

It should be noted that the signature calculation SIGN'j is performed a priori in the smart card CPj, so that the diversified keys c // (Si (,) and dKS ' ₂₎ remain confined in it. . It is the same for the calculation of the key dKS ' _2ϋ) by the module 3'.

It should also be noted that, in the two embodiments, the diversification of the pairs of mother keys MKS ^, MKS ^, MKS21, and MKS22 by the identifier of a smart card, IDj of the smart card CPj by example, which would allow to find the diversified keys is prohibited. This can be obtained simply by hardware or software means prohibiting the disclosure of these keys and their implementation for the generation of a signature. Only the signature obtained using these diversified keys can be transmitted to the outside world. According to the two embodiments, it is possible to generate so-called "authentication" data of the signature transmitted. FIG. 6 schematically illustrates the generation of such data, referenced ASIGNj for the smart card CPj.

To do this, additional diversified authentication keys, dKSA ₍ j ₎ and dKSA ₂ (i), are used, generated in the explicit manner opposite FIG. 4 and which are stored in memory M, in the positions M ₁₀ and Mu, in the example described. The generated signature SIGNj is transmitted to the input of a "T-DES", referenced 3 ". Optionally, the CGS counting data (FIG. 3) can also be injected as a data input, for example by concatenating it with the message to be signed MSG. The keys dKSA ^ and dKSA ₂ (,) are used as signature keys. The logical architecture of module 3 "is identical or at least quite similar to that of module 3 in the figure 3 used to generate the signature SIGN ,. The output of module 3 "represents the signature authentication data sought ASIGNj. This data is transmitted to the recipient (s) of the signature SIGNj. As before, the calculation is carried out inside the card to CP chip, so that the dKSA ^ and dKSA _{2 (} i ₎ keys do not leave it. In reality, the final recipient of the ASIGNj data is the CA certification authority (Figures 1 or 4). it will be shown below, a recipient, for example U _j , who wants to authenticate the signature received SIGN and ensure that it is a valid smart card CP, which issued it, submits the data of ASIGNj signature authentication to the CA certification authority, which alone can validate them since it stores the mother keys, MKSAn to MKSA ₂₂ , which were used to calculate the keys dKSA ^ and dKSA _{2 (} .).

FIG. 7 schematically illustrates the various data transmitted by a signatory smart card CPj to the recipient (s), in a preferred variant embodiment.

The transmitted data are as follows:

- MSG signed data or messages;

- optional CGS signature count data;

- signature SIGNj) - identifier IDj of the smart card CPj and / or of its holder U, -;

- CTA certificate ,, and

- ASIGNj authentication data.

It is from all this data that the addressee (s) can verify the signature SIGNj and, in the preferred variant, authenticate it using the data ASIGNj.

We will now describe the step of Verifying the signature SIGNj sent by a smart card, for example the smart card CPj, according to the two main embodiments of the method which have just been described. FIG. 8 schematically illustrates the step of verifying the signature SIGNj, generated in accordance with the first embodiment of the method according to the invention, by at least one user Uj belonging to a given group or to all of the users, s' there are no groups distinct. It should be recalled that the first embodiment authorizes verification a priori by all users, Li to U _n , listening to the message sent MSG and its signature SIGNj.

Verification consists in reconstructing the signature of the issuer and comparing it with that received. To fix the ideas, we consider the case of a smart card CPj receiving from the smart card CPj the various data illustrated in FIG. 7. The architecture of the smart card CPj is, a priori, quite similar to that of the chip card CPj, otherwise identical. This notably includes a non-volatile memory referenced M 'in which the two pairs of mother keys are stored, MKSu to MKS ₂₂ (memory positions M' ₁ , M ' ₂ , M' ₄ and M ' ₅ ), two diversified keys, dKS ^ and dKS _∑ Q) (memory positions M ' ₃ and M' ₆ ), card secret CPj, identification data IDj (Info 'and Div', memory positions M ' ₇ and M ' ₈ ), a CTA certificate, (memory position M' ₉ ) and, in a preferred variant, two authentication keys

and ûf / S-4 ₂ ( _/ ) (memory positions M'10 and M'n).

A first diversified key, referenced dKS < _\ is calculated from the mother keys MKSu and

and of the identifier IDj received from the chip card CP ,, by using a symmetrical algorithm, preferably a "T-DES", referenced 5a. The identifier IDj is injected on the data entry. The mother keys MKSu and MKS ^ are transmitted to the key entries. A second diversified key is calculated in the same way using the "T-DES" 5b, from the mother keys MS ₂ ι and MKS ₂₂ and also from the identifier received IDj. The calculated diversified keys, dKS ^ and dKS _∑ , can be temporarily stored in registers, 6a and Qb, or in positions of a random access memory (not shown) which is usually provided with a smart card. A third "T-DES", referenced 5c receives as keys the keys previously calculated and on its data input, the message MSG transmitted by the chip card CPj, as well as possibly the counting word CGS signature generation . The data output from the module 5c, referenced SIGN, is assumed to represent the signature SIGNj sent by the smart card CPj. The corresponding data can be stored in a register 6c or a position of RAM. A comparison operation is carried out performed by the module 7. If the reconstructed signature SIGN is identical to the received signature SIGNj, the result (signal or data on the output S) is positive and the latter authentic. The chip card CP _j also receives the certificate CTA, from the chip card CPj (see FIG. 7). The latter can be checked by module 8 using the public key Kp issued by the CA certification authority (Figures 1 and 4). As has been recalled, the public key Kp is made available to all the users U _j , at least within the same group if there are several distinct groups. Data for verifying the CTA certificate is available on output S ¹ .

For reasons of clarity of the drawing, the "T-DES", 5a to 5c, the registers, 6a to 6c, the comparison members 7 and of verification 8 have been represented on the outside of the chip card CPj. It goes without saying that, as before, these are installed in the smart card, the diversified keys and the results of the calculations should not be disclosed to the outside world. The functions performed may also call in whole or in part on software.

The verification of a signature generated in accordance with the second embodiment of the method according to the invention will now be described with reference to FIG. 9. The elements common to the preceding figures, in particular to FIG. 8, bear the same references and will not be re-described as necessary.

As before, a diversified key, dKS ^, is calculated from the identifier IDj received from the smart card CPj. On the other hand, the diversified key dKS ₂ ^, stored in the chip card'CP, is directly used as a signature key. It is assumed that the key dKS _{2 (/ j} has been obtained by diversification from the mother keys MKS _{2 \} and MKS ₂₂ and the identifier ID _j provided by the smart card CPj. The key dKS ₂₎ and the calculated key dKS are transmitted to the key inputs of the "T-DES" 5c, which receives on its data input, as before, the message transmitted MSG and, optionally, the signature count word CSG. The rest of the process is identical to that described for the first embodiment (Figure 9), and there is no need to re-describe it in detail.

The CTA certificate is verified in the same way as before.

In both cases the calculated signature, SIGN is never delivered to the outside world. Only the result of the comparison can be disclosed.

In summary of the above, since neither the diversified keys, secret of each smart card, for example CP, nor the results of the signature calculations come out of the smart cards, it follows that the system is not repudiable. We will now describe, with reference to FIG. 10, the verification of the authenticity of the signature SIGN ,.

Any user U _j having verified a signature generated by another user, for example Uj, can submit to the certification authority CA the identifier of the signatory IDj, the certificate of this identifier CTA, the signature SIGN, the data of ASIGNj authentication and optional CGS signature generation count data.

From this data, the CA certification authority recalculates, from the pairs of mother keys MKSA to MKSA ₂₂ and the diversifier ID, -

(after checking the certified identity) of the signatory smart card CPj and / or of its bearer Uj, diversified keys dKSA ^ and dKSA ^, to control the authentication authentication data ASIGNj.

The mother key pairs MKSA -MKSAπ, on the one hand, and MKSA21- MKSA ₂₂ , on the other hand, are transmitted to the key inputs of two "T-DES" modules, 9a and 9b, which receive, on their inputs IDj identifiers. The outputs of these modules provide the diversified signature authentication keys, dKSA ^^ and dKSA ₂ (, ₎ , keys transmitted to the key inputs of a third "T-DES", referenced 9c. The latter receives on its data input, the SIGN signature, and the optional signature generation counting data CGS. The ASIGN data present on the output of the "T-DES" 9c are supposed to represent the reconstituted ASIGN data. They are therefore compared with the latter in a comparator module 9c. The result of the comparison, positive or negative, is available on the output S "of the module 9d. This result is returned to the user who requests it, for example the user Uj, signed by the keys dKSA ^ and dKSA _∑ ij) and a "T-DES" 9e. Naturally, these keys, dKSA ^ and dKSA (,), are not transmitted directly by the user Uj, but recalculated by the certification authority CA, by application of "T-DES" (not shown) and to the using the mother keys MKSA -MKSA ^, on the one hand, and MKSA rMKSA ₂ 2, on the other hand, and the identifier ID _j of the user Uj, in a manner analogous to the calculation of the keys dKSA ^ and dKSA _{2 (} , ₎ . The signed result R, at the output of the "T-DES" 9e, can then be deciphered by the user U _j using his own authentication keys dKSAi _Q) and dKSA _∑ ®, by applying a " T-DES "additional (not shown).

Optionally, a password or similar identification ("PIN-code, etc.) may be required to further enhance the security of the process.

On reading the above, it is easy to see that the invention achieves the goals it has set for itself.

It provides, in particular in its preferred embodiment, great security and the possibility of obtaining non-repudiation of the signatures issued, without having to resort to asymmetric encryption methods within smart cards, and more generally light on-board electronic chip terminals. As a result, it becomes possible to use electronic chips provided with standard calculation means and memory. In particular, the electronic chip need not be provided with a mathematical co-processor.

It follows that the cost and the complexity induced by the process remain within acceptable limits for so-called "general public" applications.

It should be clear, however, that the invention is not limited to only the examples of embodiments explicitly described, in particular in relation to FIGS. 1 to 10.

In particular, although the asymmetric algorithm "RSA" and the symmetrical algorithm of triple type "DES" are particularly interesting, the invention is in no way limited to these algorithms alone. Other algorithms, both asymmetrical and symmetrical, respectively, are quite possible. Choosing an algorithm particular is only a technological choice within the reach of a person skilled in the art, depending in particular on the precise application targeted.

Claims

1. Method for generating a signature which cannot be repudiated by a first entity of a set, in particular by an on-board system with an electronic chip comprising at least non-volatile memory means and calculation means, said signature being intended to be disseminated and verified by at least one of said entities of the assembly, characterized in that it comprises a preliminary phase comprising at least the following steps:

- the storage in said non-volatile memory means (M) of two pairs of so-called "mother" signature keys (MKS -MKS- [ ₂ , MKS ₂ r MKS ₂₂ ), common to all said entities (CP „CPj) ;

- The generation, from at least one of said pairs of "mother" signature keys (MKS -MKSi∑) and a unique identifier (ID,), specific to said first entity (CP,), of a first so-called diversified signature key (dKS ^), by applying a symmetric cryptography algorithm (1) and storing said diversified key in said non-volatile memory means (M);

- storing said unique identifier (IDj) in said non-volatile memory means (M);

- the generation by an additional entity called "certification authority" (CA) of a certificate (CTA) constituting an authorization to sign for said first entity (CP,), said certificate (CTA) being obtained from at least said identifier (IDj) and a private encryption key (K _A ) held by said certification authority (CA), by application of an asymmetric cryptography algorithm (2), and the storage of said certificate (CTA) in said means of non-volatile memory (M); and

the distribution, by said certification authority, of a public signature verification key (K _P ) to all or part of said entities (CPj, CPj) of the assembly and a subsequent phase comprising at least the following steps: the generation of said non-repudiable signature (SIGNj) from said first diversified signature key (dKS ^ (, j), of a second diversified signature key (dKS ₂ (j), dKS ' ₂ (j) ) and of data to be transmitted (MSG) intended for at least one of said entities (CPj) of the set, by application of a symmetric encryption algorithm (3, 3 '); and

- the distribution to at least one of said entities (CPj) of all of at least said data (MSG), said signature (SIGNi), said identifier (/ D,) and said certificate (CTA) .

2. Method according to claim 1, characterized in that said second diversified signature key (dKS ₂ (ij) is generated, during said preliminary phase, from said second pair of "mother" signature keys (MKS ₂ rMKS ₂₂ ) and from said unique unique identifier (IDj) to said first entity (CPi), by applying a symmetric cryptography algorithm (1), and in that said second diversified signature key (dKS ₍ , ₎ ) is stored in said non-volatile memory means (M).

3. Method according to claim 1, characterized in that said second diversified signature key (dKS ' ₂ (j ₎ ) is generated from said second pair of "mother" signature keys (MKS ₂ MKS ₂ 2) and d 'a unique identifier (IDj) specific to one of said entities (CPj), recipient of said non-repudiable signature (SIGNi), by application of a symmetric cryptography algorithm (3').

4. Method according to claim 1, characterized in that it comprises an additional step of generation, during said preliminary phase, by said certification authority (CA), of a pair of additional signature keys called authentication (c CSAi (o, dKSA _∑ ^) from two pairs of signature keys known as "mothers"

specific to this authority (CA) and said identifier (IDj) specific to said first entity (CP,), by application of a symmetric encryption algorithm (1 ′, 1 ″), and in that said pair of keys authentication (dKSA ^^, αf / CSA)) is stored in said non-volatile memory means (M).

5. Method according to claim 4, characterized in that it comprises a step of generation, by said first entity (CPi), of so-called signature authentication data (ASIGNj) from said pair of additional signature keys d authentication (dKSA ^, dKSA ₂ (,)) and at least said non-repudiable signature (SIGNi), and in that said signature authentication data (ASIGN1) are broadcast to at least one of said entities (CPy) of the set.

6. Method according to claim 1, characterized in that it comprises a phase of verification of said non-repudiable signature (SIGNi) by at least a second entity (CPy) of said set comprising at least the following steps:

- generation of first and second diversified signature keys

(dKS- _\ , dKS ₂ ), each of said signature keys being generated from said pairs of "mother" keys (Sι M / CS ₁₂ , MKS ₂ rMKS _Z 2) stored in said non-volatile memory means (M ) and said identifier (IDi) broadcast by said first entity (CP,), by application of a symmetric cryptography algorithm (5a, 5b);

- the reconstitution of a signature (SIGN), from these said diversified signature keys (dKS, 5 ₂ ) and at least of said data (MSG) transmitted by said first entity (CPi), by application of a symmetric cryptography algorithm (5c); and

- verification of said non-repudiable signature (SIGNi) generated by said first entity (CP,) by comparison (S, 7) thereof with said reconstituted signature (SIGN), so as to validate said transmitted data (MSG) .

7. Method according to claim 6, characterized in that it comprises a step of verification (8) of said certificate (CTA,) transmitted by said first entity (CPi), using said public signature verification key ( Kp) issued by said certification authority (CA).

8. Method according to claim 7, characterized in that said set is partitioned into several distinct groups of entities and in that said authority certification (CA) distributes to each of said groups a different public key.

9. Method according to claim 5, characterized in that it comprises a phase of verification of said authentication data comprising at least the following steps:

- the submission to said certification authority (CA), by at least one of said entities (CPy) of the set, of said authentication data (ASIGNi) received from said first entity (CP,);

- The generation by said certification authority (CA) of first and second diversified verification keys (dKSA ^, dKSA ₂ ), each of said verification keys being generated from said pairs of "mother" keys (MKSAu-MKSA _Z , MKSA ₂ rMKSA ₂₂ ) specific to said certification authority (CA) and said identifier (ID,) disseminated by said first entity (CPi), by application of a symmetric cryptography algorithm (9a, 9b);

- the reconstitution of signature authentication data (ASIGN), from these so-called diversified verification keys generated (dKSA-, dKSA ₂ ) and at least said signature (SIGNi) transmitted by said first entity (CPi), by application of a symmetric cryptography algorithm (9c); and

- verification of said signature authentication data (ASIGNi), transmitted by said first entity (CPi), by comparison (S ", 9d) of these with said reconstituted signature authentication data (ASIGN), so to validate them; and

- the retransmission of the result (S ") of the comparison to said entity (CPy) having submitted said signature authentication data (ASIGNi).

10. Method according to claim 4, characterized in that it comprises steps of generation (4) of signature generation counting data (CSG) and in that said signature generation counting data (CSG) are used together with said data to be transmitted (MSG) to generate said non-repudiable signature (SIGNi) and / or to this signature (SIGNi) to generate said signature authentication data (ASIGNi).

11. Method according to claim 1, characterized in that said symmetric cryptography algorithms (1, 3) are constituted by triple "DES".

12. Method for generating a non-repudiable signature by a first entity (CPi) of a set, in particular by an on-board system with an electronic chip comprising at least non-volatile memory means and calculation means, said signature being intended to be broadcast and verified by at least one of said entities (CPj) of the set, characterized in that it consists in generating said non-repudiable signature (SIGNi) from a first diversified signature key (dKS ^) obtained from at least one pair of "mother" signature keys (MKSn-MKSπ) common to all the entities (CPi, CPj) and a unique identifier (IDi), specific to said first entity (CPi ) by applying a symmetric cryptography algorithm (1), a second diversified signature key (dKS≤ ©, dKS ' ₂ (j)) and data to be transmitted (MSG) intended for at least one of said entities ( CPy) of the set, by application of a cry algorithm symmetrical page (3, 3 '), the signature being intended to be distributed to at least one of said entities (CPj) of the set with at least said data (MSG), said identifier (ID,) and a certificate ( CTA,) constituting an authorization to sign for the first entity (CPi) obtained from at least said identifier (IDi) and a private encryption key (K _A ) held by a certification authority (CA), by application of 'an asymmetric cryptography algorithm (2).

13. A method of personalizing an entity (CPi) of a set for the purpose of implementing the method of generating a signature which cannot be repudiated by said entity (CPi) according to claim 12, characterized in that it comprises the following steps:

- the storage in said non-volatile memory means (M) of two pairs of so-called "mother" signature keys (MKS -MKS ₂ , MKS ₂ r MKS22), common to all of said entities (CPj, CPj); the generation, from at least one of said pairs of "mother" signature keys (MKSu-MKS ^) and of said unique identifier (IDi), specific to said first entity (CP,), of said first signature key diversified (dKS ^), by applying a symmetric cryptography algorithm (1) and storing said diversified key in said non-volatile memory means (M);

- storing said unique identifier (IDi) in said non-volatile memory means (M);

- the storage in said non-volatile memory means (M) of said certificate (CTAi) generated by an additional entity called "certification authority" (C4) constituting an authorization to sign for said first entity (CPi), said certificate (CTA) ) being obtained from at least said identifier (IDi) and said private encryption key (K _A ) held by said certification authority (CA), by application of an asymmetric cryptography algorithm (2).

14. On-board electronic chip system intended for the generation of a non-repudiable signature intended to be disseminated and verified by at least one second on-board system of a set, each of said on-board systems comprising at least ήon-volatile memory means and calculation means installed in said electronic chip, characterized in that said non-volatile memory means (M) store at least two pairs of so-called "mother" verification keys (MKS -MKS, MKS ₂ rMKS ₂₂ ), a identifier (IDi) specific to said on-board system (CPi), at least one first verification key known as "diversified" (dKS ^), generated from one of said pairs of verification keys "mothers" (MKS _U -MKS _M ) and said identifier (ID,), by application of a symmetric cryptography algorithm (1), and a certificate (CTAi), generated by an entity called "certification authority" (CA) from a private key of signature (K _A ) d held by said certification authority (CA) and said identifier (IDi), by application of an asymmetric cryptography algorithm (2), and in that it comprises means of generation (1) of said signature by application of a symmetric cryptography algorithm (3, 3 '), making use of said first diversified signature key (αf / Si ₍ , ₎ ), of a second diversified signature key (dKS _{2 (} j), dKS' _{2 ( j)} ) and data to be disseminated and to sign (MSG), for transmission to at least one second on-board system (CPy) of said set.

15. The system as claimed in claim 14, characterized in that said memory means (M) further store a pair of additional verification keys known as authentication keys (dKSA ^, KSAn _j j), generated by said certification authority (CA ) from a pair of so-called "mother" verification keys (MKSA -MKSA ^, MKSA ₂ rMKSA ₂ 2) specific to this certification authority (CA) and said identifier (IDi) specific to said first entity (CP, ), by applying a symmetric encryption algorithm (1 ', 1 ").

16. System according to claim 14, characterized in that it is constituted by a smart card (CPi).